1. Field of the Invention
This invention relates to an eyepiece optical system used in an imaging device having a finder optical system or in the finder optical system, and in particular, to an eyepiece optical system of a finder suitable for a small-sized and slim-type imaging device.
2. Description of Related Art
Conventional eyepiece optical systems of this type are represented by an optical system that an intermediate-image-side surface of a lens placed immediately behind an intermediate image is configured as a convex surface (refer to, for example, Japanese Patent Kokai No. Hei 11-64744; pp. 1-7, FIGS. 1, 3, 4, and 5), an optical system that a lens placed immediately behind the intermediate image is configured as a negative lens (refer to, for example, Japanese Patent Kokai No. Hei 10-311957; pp. 2-7, FIGS. 1, 3, 4, and 5), a retrofocus-type optical system (refer to, for example, Japanese Patent Kokai No. Hei 7-295034; pp. 1-6, FIGS. 1 and 2), and a path bending-type optical system (refer to, for example, each of Japanese Patent Kokai Nos. Hei 7-5360 and Hei 8-22048; pp. 1-2, FIG. 1).
The eyepiece optical system set forth in each of Kokai Nos. Hei 11-64744 and Hei 10-311957 is constructed with a telephoto-type system which includes, in order from an intermediate imaging plane of a real image formed by an imaging optical system, a positive lens unit and a negative lens unit.
The eyepiece optical system set forth in Kokai No. Hei 7-295034 is such that a negative lens is placed not immediately behind the intermediate image (a finder screen 6) but behind a prism (a pentaprism 5).
The eyepiece optical system disclosed in Kokai No. Hei 7-5360 is merely constructed with a combination of positive lenses (a reflecting member P3 and an eyepiece G4).
The eyepiece optical system disclosed in Kokai No. Hei No. 8-22048 is such that a diopter adjusting optical system (a field lens component 12) placed in the proximity of the intermediate imaging plane has positive power.
The eyepiece optical system according to the present invention is interposed between the positions of an intermediate image and a pupil in a finder and comprises, in order from the intermediate-image side, a first lens unit having a negative lens located at the most intermediate-image-side position and a second lens unit including a path-bending optical member and having positive power as a whole, satisfying the following condition:
xe2x88x9220 less than sf1 less than 0xe2x80x83xe2x80x83(1)
where sf1 is the shaping factor of the negative lens and is expressed as (r11+r12)/(r11xe2x88x92r12), where r11 is the radius of curvature of the intermediate-image-side surface of the negative lens and r12 is the radius of curvature of the pupil-side surface of the negative lens.
This and other features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.